Information overload acts ‘to dim the lights’ on what we see

17 March 2014

Too much visual information causes a phenomenon known as ‘load induced blindness’, with an effect akin to dimming the lights, reports a new UCL study.

The new findings could be used to identify high-risk situations in all
walks of life and look at ways to mitigate times of highest risk. These
techniques could be used to understand everyday problems such as why you might
bump into a lamppost on a busy street or even to assess the demanding
information loads faced by pilots and surgeons.

More than half of all air crashes are down to pilot error, as the
overwhelming amount of information faced by pilots makes them more likely to
miss things. The research shows that when people have to deal with lots of
visual data, their ability to spot critical information is lessened as if light
levels of the image they need to detect were significantly lowered.

In the experiment, volunteers completed a sensory memory task that either
involved encoding the colour of a single square, ‘low load’, or both the colours
and positions of six different coloured squares, ‘high load’ over many
computerised displays that were rapidly flashed up. In addition, while they
encoded the coloured squares, a stripped black and white image appeared in the
surrounding area. The striped patches had lines in different orientations, representing
the building blocks of shapes. Participants were asked to detect whether the orientation
of the lines was rotated clockwise or anticlockwise.

Participants correctly spotted rotations with 95% accuracy during the low
load task but only 64% accuracy during the high load task. The contrast of each
image was varied throughout the trials, representing a change in the level of
light illuminating each image. The results showed that participants required the
equivalent of 50% more light contrast on average to spot orientation rotations under
high load conditions.

“Spotting the appearance of any critical image in the environment depends
on its level of contrast as our neurons are more responsive to stronger
contrasts” explains Professor Nilli Lavie (UCL Institute of Cognitive Neurosciene), who led the research. “In high
load situations people needed significantly more light contrast to spot
rotations with a threshold of 27% contrast, compared with 18% contrast for low
load conditions. In other words the
neuron responses required more contrast and the image appeared dimmer in the
high load. For a pilot, this could make the crucial difference between whether
or not they spot that the hand of a dial has moved or a warning light has come
on, or see something through the window that was not detected by instruments.”

The study involved 14 healthy volunteers with normal vision, each of whom
completed 384 trials in total. The effects were consistent across the group,
and the images used in the trial were specifically designed to investigate the
effects of light contrast.

“What’s fascinating is that the relationship between image contrast and
people’s ability to spot things is shifted in high-load scenarios in a pattern
that is the very same as if the image’s level of light contrast was turned down,”
says Professor Lavie. “The neurons’ response to light contrast has a very
particular function, with highest response at the crucial mid-range zone, and
the effect of load followed the same function. This suggests load caused the
same effect on the neurons’ response as dimming the actual image light
contrast.”

Further investigating the ‘load blindness’ induced by information
overload could offer future strategies to minimise human error in demanding
jobs.

“We need to identify and understand the most attention-demanding
situations that people face so that we can look at ways to address the risks,”
explains Professor Lavie. “Surgeons are another group who must deal with high
levels of information, so it would be useful to evaluate the stages of surgical
procedures that are the most vulnerable to information overload. You could then
look at installing appropriate preventative measures to mitigate these risks,
whether that’s changing training, equipment or staff roles.”